The present invention relates to the field of alarm systems and particularly to an intrusion detection apparatus for use in detecting intrusions into homes, stores, factories or other enclosures.
Prior devices for detecting intrusions have relied upon many different principles. For example, contact switches have been mounted on each door and window of an enclosure. Upon opening a door or window, the switch is actuated to set off an alarm. Similarly, radiation devices have been employed wherein an entry into an enclosure causes the radiation field to be disturbed thereby setting off an alarm.
Other devices have relied upon the differential air pressure between an enclosure and the external environment. Such an apparatus is described in U.S. Pat. No. 3,829,851. An improved differential pressure device is described in the above cross-referenced patent application.
While some of the above instrusion detecton devices have a high level of sensitivity, they still exhibit problems in reliability. The reliability problem generally results in too many false alarms. In general, all of the intrusion alarm systems which have been on the market suffer from a level of false alarms which is too high.
In view of the above background of the invention, there is a need and it is an object of the present invention to provide an improved intrusion alarm system which is highly sensitive to intrusions while having an improved ability to distinguish between intrusions and false alarm conditions.